Answer:
C. The mean for brand B is higher than brand A.
Explanation:
What we're looking for is the true statement of these 4.
We already know B is out, because there were 11 lightbulbs on brand B, and 10 on brand A.
Because of that, A is also out, because the means cannot be the same.
As a result, only C and D remain.
Now, add the 10 dots on brand A.
((1000 * 1) + (1100 * 2) + (1200 * 3) + (1300 * 4))/10
(1000 + 2200 + 3600 + 5200)/10
(3200 + 3600 + 5200)/10
(6800 + 5200)/10
12000/10
Brand A has an average of 1200 hours/lightbulb
Then, add the 11 on brand B
((1400 * 1) + (1500 * 4) + (1600 * 2) + (1700 * 1) + (1800 * 1) + (1900 * 1))/11
(1400 + 6000 + 3200 + 1700 + 1800 + 1900)/11
(7400 + 3200 + 1700 + 1800 + 1900)/11
(10600 + 1700 + 1800 + 1900)/11
(12300 + 1800 + 1900)/11
(14100 + 1900)/11
16000/11
Brand B has an average of 1454 hours 27 minutes 16 seconds 364 milliseconds/lightbulb
Comparing the two averages, we come to the realization that D is out because Brand A's average was less than Brand B's.
That leaves C as our answer.